Switchable mirror display patents EP0933663B1 (Sekiguchi et al.; 4 Aug. 1999) and JP3419766 (Adachi et al.; 16 Nov. 2001) describe the use of reflective polariser films (e.g., dual brightness enhancement films, or “DBEFs”) sandwiched between a first and second image display. These display devices can be electrically switched between a normal image display mode and a mirror mode whereby ambient light is reflected from the DBEF to produce a mirror mode.
U.S. Pat. No. 7,495,719B2 (Adachi et al.; 24 Feb. 2009) describes a display device capable of being electrically switchable between a state that displays a high-quality image (normal mode) and a mirror mode. The mirror mode produces an easy-to-view reflection image suitable for a person to view his/her own face or figure. With reference to FIG. 1 of Adachi, the display device has an image display portion 1000, a reflective polarization selection member 300, a transmission polarization axis variable portion 400, and an absorbing polarization selection member 500, which are successively disposed. The image display portion 1000 includes an absorbing polarization selection member 208 that transmits a linear polarization component of a predetermined direction and absorbs a linear polarization component of a direction orthogonal thereto, and the absorbing polarization selection member 208 is disposed at the reflective polarization selection member 300 side. U.S. Pat. No. 5,686,979 (Weber et al.; 11 Nov. 2011) describes the use of a standard backlight, a reflective polariser film (DBEF), a first simple switchable liquid crystal (LC) panel and a second liquid crystal display (LCD) capable of showing images. These components are assembled to yield a display system that can be switched between a transmissive display mode that utilises the backlight and a reflective display mode that does not use the backlight. A reflective LCD is particularly useful for viewing images in high ambient lighting conditions.
U.S. Pat. No. 5,686,979 also describes the use of reflective polariser films (DBEFs) and a single image display to yield a display system capable of conveying text and monochrome pictures.
WO2014002402A1 (Smith et al.; 3 Jan. 2014) describes the use of reflective polariser films (DBEF) sandwiched between a first and second image display. The display system is capable of multiple image functions.
The design and operation of parallax barrier technology for viewing 3D images is well described in a paper from the University of Tokushima Japan (“Optimum parameters and viewing areas of stereoscopic full colour LED display using parallax barrier”, Hirotsugu Yamamoto et al., IEICE trans electron, vol. E83-c no 10 Oct. 2000).
FIG. 1 shows the basic design and operation of parallax barrier technology for use in conjunction with an image display for creating a 3D display. The images for the left eye and right eye are interlaced on alternate columns of pixels of the image display. The slits in the parallax barrier allow the viewer to see only left image pixels from the position of their left eye and right image pixels from the position of their right eye.
The same autostereoscopic 3D effect as shown in FIG. 1 can be achieved by using lenticular lenses. Each lens is substantially equivalent to a parallax barrier slit. FIG. 2 shows a conventional 3D system comprised of lenticular lenses and an image display.
The technologies illustrated in FIG. 1 and FIG. 2 can be configured to provide a high quality 3D mode. However, many applications exist whereby a display is also required to operate in a high quality 2D mode. Using the technologies illustrated in FIG. 1 and FIG. 2 would yield a 2D image with half the native resolution of the image display—this is highly undesirable. For the image display to show an image with 100% native resolution in the 2D mode, the parallax optics (parallax barrier, lenticular etc.) must be switchable between a first mode that provides substantially no imaging function (2D mode) to a second mode of operation that provides an imaging function (3D mode).
An example of a switchable parallax barrier technology is disclosed in U.S. Pat. No. 7,813,042B2 (Mather et al.; 12 Oct. 2010). However, switchable parallax barrier technology has the disadvantage that the parallax barrier absorbs light in the 3D mode, reducing transmission by ˜65%. This inefficient light usage is a disadvantage since the 2D mode and 3D mode will have a significantly different brightness. Boosting the brightness of the 3D mode can be achieved at the expense of increased power consumption, which is undesirable, especially for mobile products.
A liquid crystal graded refractive index lens (LC GRIN lens) is a switchable lens that uses conventional liquid crystal display (LCD) manufacturing processes. 3D display systems that use LC GRIN lenses have been disclosed by US2007296911A1 (Hong; 27 Dec. 2007), U.S. Pat. No. 7,375,784 (Smith et al.; 20 May 2008) and “30.3 Autostereoscopic Partial 2-D/3-D Switchable Display” by Takagi et al (SID DIGEST 2010 pp 436).
A further example of an optical element that provides a high quality 2D mode and a high quality 3D mode is disclosed in GB1103815.5 (Smith et al; filed GB 7 Mar. 2011). To enable the 3D mode, the optical element disclosed in GB1103815.5 includes an array of GRIN lenses, with each GRIN lens separated from the next by a region of parallax barrier.
Bistable Liquid Crystal Displays are described by Bryan-Brown et al. “Grating Aligned Bistable Nematic Device”, Proc SID XXVIII 5.3, pp 37-40 (1997) and patents U.S. Pat. No. 6,249,332 (Bryan-Brown et al.; 19 Jun. 2001), U.S. Pat. No. 7,019,795 (Jones; 28 Mar. 2006) and U.S. Pat. No. 6,992,741 (Kitson et al, 21 May 2002). A bistable LCD has two energetically stable configurations of the liquid crystal molecules. Power is only required to switch from a first energetically stable state to the second energetically stable state. Consequently, a bistable LCD can be passively addressed with a first image and power is only required to display a second image that is different from the first image. A bistable LC mode may be combined with optical components to enable a reflective bistable LCD. A reflective bistable LCD is particularly useful for viewing images in high ambient lighting conditions. A reflective bistable LCD is particularly useful for display applications requiring very low power consumption.
The principle and operation of Supertwisted Nematic (STN) Displays have been fully described by many different sources, including “Optics of Liquid Crystal Displays” pp. 194 by Yeh and Gu (Wiley, 1999). Supertwisted Nematic Displays employ a liquid crystal mode that can be passively addressed in order to yield an image.
The principle and operation of Bistable Twisted Nematic (BTN) Displays have been fully described by many different sources. A review of the BTN LC mode is described in “0°-360° bistable nematic liquid crystal display with large dΔn” by X. L. Xie et al, Journal of Applied Physics, Vol. 88, No. 4, p. 1722. Bistable Twisted Nematic Displays employ a liquid crystal mode that can be passively addressed in order to yield an image.
The principle and operation of Ferroelectric Liquid Crystal Displays (FLC) have been fully described by many different sources including U.S. Pat. No. 4,840,463 (Clark et al.; 20 Jun. 1989) and U.S. Pat. No. 4,958,916 (Clark et al.; 25 Sep. 1990). Ferroelectric Liquid Crystal Displays employ a liquid crystal mode that can be passively addressed in order to yield an image.
U.S. Pat. No. 6,445,434 describes the use of an additional liquid crystal layer to enable switching between a wide angle public viewing mode and a narrow angle private viewing mode.